Geology of Late Miocene clayey sediments and distribution of palaeosol clay minerals in the north-eastern part of the Cappadocian Volcanic Province (Araplı-Erdemli), central Anatolia,

The study area is situated in the Araplı-Erdemli (Kayseri) area in the north-eastern part of the Cappadocian Volcanic Province (CVP), central Anatolia. The Late Miocene series comprises lacustrine and fluvial deposits interbedded with ignimbrites and lava flows. The Late Miocene Mustafapaşa member of the Ürgüp Formation comprises yellow to red mudstone that alternates with thin sandstone beds in the north-eastern part of the CVP.

http://journals.tubitak.gov.tr/earth/ (2013) 22: 427-443

© TÜBİTAK doi:10.3906/yer-1112-1

Geology of Late Miocene clayey sediments and distribution of palaeosol clay minerals in the north-eastern part of the Cappadocian Volcanic Province (Araplı-Erdemli), central

Anatolia, Turkey

1 Department of Geological Engineering, Eskişehir Osmangazi University, TR-26480 Eskişehir, Turkey

2 Department of Geological Engineering, Niğde University, TR-51200 Niğde, Turkey

1 Introduction

Since the last quarter of the 20th century,

palaeoclimatological changes have been studied using

sedimentary-petrographic data from marine (Thiry

2000; Ehrmann et al 2005; Berrocoso et al 2008) and

non-marine sediments (Singer 1984; Bellanca et al 1992;

Prudêncio et al 2002)

This study area covers 100 km2 in the north-eastern

part of the Cappadocia region of central Anatolia (Turkey)

The occurrence of a large clay deposit in the Late Miocene

Mustafapaşa member of the Ürgüp Formation, the altered

Cemilköy ignimbrite, and the palaeosols between the

Gördeles and Kızılkaya ignimbrites are first described in

the area in this work The Mustafapaşa member consists

of alternating conglomerate, sandstone, and mudstone

The altered Cemilköy ignimbrite, red palaeosols, vertisols and mature, white palaeosol layers developed between the Cemilköy and Gördeles ignimbrites Red palaeosols, mature brown and red palaeosol levels occur between the Gördeles and Kızılkaya ignimbrites

The Cappadocian Volcanic Province in central Anatolia has been previously studied in order to elucidate the stratigraphy (Pasquaré 1968; Schumacher &

Mues-Schumacher 1997; Le Pennec et al 2005; Viereck-Goette

et al 2010), the relationship between magmatism and tectonism (Innocenti et al 1975; Pasquaré et al 1988; Göncüoğlu & Toprak 1992; Temel et al 1998; Toprak

1998), the mineralogy and origin of clay minerals (Gürel

& Kadir 2006; Gürel & Kadir 2008; Ertek & Öner 2008), and ecosystem changes (Lepetit & Viereck-Goette 2007)

Abstract: The study area is situated in the Araplı-Erdemli (Kayseri) area in the north-eastern part of the Cappadocian Volcanic Province

(CVP), central Anatolia The Late Miocene series comprises lacustrine and fluvial deposits interbedded with ignimbrites and lava flows The Late Miocene Mustafapaşa member of the Ürgüp Formation comprises yellow to red mudstone that alternates with thin sandstone beds in the north-eastern part of the CVP This unit continues upward through the Cemilköy ignimbrite palaeosol layers (comprising altered Cemilköy ignimbrite, vertisol and well-developed palaeosol layers), the Gördeles ignimbrite and red palaeosol layers, and includes two fallout levels; it is overlain by the Kızılkaya ignimbrite The Mustafapaşa member is dominated by smectite±illite±chlorite, whereas the altered Cemilköy ignimbrite is predominantly kaolinite±smectite±chlorite The underlying lower level of the Gördeles ignimbrite contains palaeosol layers, and continues upward through smectite-dominated layers Alteration of feldspars and glass shards in the Cemilköy and Gördeles ignimbrites resulted in the depletion of soluble alkaline elements (such as Ca, Na and K) from these ignimbrites downward to the Mustafapaşa member, and palaeosol levels (Bayramhacılı member) in the Araplı area favoured precipitation of smectite in an alkaline environment However, the absence of these elements in these ignimbrites may have resulted in the enhancement of Al+Fe/Si-favoured precipitation of kaolinite in an acidic environment Conversely, palaeosol of the Erdemli area consists of smectite±illite±chlorite Micromorphologically, flaky smectite rims illite in both the Araplı and Erdemli areas and this can

be explained by the release of K and Al during desorption of feldspar Additionally, higher Ni, Co and Cr2O3 values in the mudstone samples of the Mustafapaşa member and palaeosol levels, the presence of iron oxide and partially chloritised pyroxene and hornblende, together with ophiolitic and metamorphic grains, indicate that the basin also accumulated ophiolitic and metamorphic rock fragments

in its sediment supply This suggests that the Araplı area in the southern part of the CVP has undergone erosion, and that the present-day Erdemli area was close to the shallow-lake depositional environment of the northern part of CVP.

Key Words: Palaeosol, ignimbrite, smectite, kaolinite, central Anatolia.

Received: 05.12.2011 Accepted: 19.06.2012 Published Online: 06.05.2013 Printed: 06.06.2013

Research Article

Prior to the present study, no information about the

clay sedimentology and mineralogy of the Late Miocene

units between the Araplı and Erdemli areas was available

Therefore, the aim of this paper is to describe the geology,

mineralogy, and geochemistry of the north-eastern section

of the CVP sediments, and to discuss the genesis of the

clay deposits and their depositional environment

2 Local geological setting

Basement rocks of the Araplı area comprise Palaeozoic

mica schists and marbles and Late Cretaceous ophiolitic

rocks which tectonically overlie the older units (Figure

1) The Oligocene Yeşilhisar conglomerate contains

metamorphic and ophiolitic rock fragments, and

the Palaeogene-Neogene series discordantly overlies

basement rocks This unit is discordantly overlain by the

Neogene Ürgüp Formation (Figure 2) The Mustafapaşa

member (Late Miocene) is the earliest unit of the Ürgüp

Formation in the Araplı area, comprising alternating

conglomerate, sandstone and mudstone laid down in

a lacustrine environment The Late Miocene Cemilköy

ignimbrite overlies the Mustafapaşa member and

separates it from the overlying Bayramhacılı member

(Pasquaré 1968) The Bayramhacılı member is split into

two sub-members (the Lower and Upper Bayramhacılı) by

the Gördeles ignimbrite The Upper Bayramhacılı unit is

overlain by the Kızılkaya ignimbrite (Gürel & Kadir 2006)

These volcaniclastic units are discordantly overlain by

Quaternary white travertine (outside the study area) and

alluvium

3 Description of stratigraphic sections

Five north–south stratigraphic sections have been studied,

in the study area between the villages of Araplı and Erdemli

(Kayseri)(Figure 3)

3.1 Araplı - Section I

This section begins with palaeosol layers Each palaeosol

is mud containing pumice and plant rootlets These

palaeosol horizons are overlain by a white fallout-I

unit, containing more than 80% pumice After 3-4 m

of covered section, the section continues upward with

similar palaeosol layers, and the fallout-II layer contains

lithic clasts and pumice (A1-3) This horizon is overlain

by more palaeosol layers which begin with white,

pumice-bearing palaeosol, and continue upward with palaeosols

containing brown to light brown, fine-grained lithic clasts,

plant rootlets and pumice These units are overlain by the

pale grey Gördeles ignimbrite, comprising mainly lithic

pumice This ignimbritic unit is overlain by fine-grained

and coarse-grained palaeosol levels, respectively Finally,

the massive and columnar-jointed Kızılkaya ignimbrite

sits at the top of this section

3.2 Araplı – Section II

This section has a basal fine-grained, clayey palaeosol layer, then a fine-grained and lithic-clast-bearing palaeosol layer, deposited above the Yeşilhisar conglomerate or ophiolitic rocks These units are overlain by the pale grey Cemilköy ignimbrite (Figure 4a), comprising mainly lithic pumice and altered Cemilköy ignimbrite (Figure 4b,c) layers These layers are overlain by palaeosol layers, beginning with a massive, clayey, fine-grained palaeosol and continuing with a red, fine-grained palaeosol layer and a grey vertisol layer (Figure 4d) These units are overlain by fallout-II deposits with lithic-pumice and lithic clasts and

a red, fine-grained, clayey palaeosol horizon (Figure 4e) These are overlain by the pale grey Gördeles ignimbrite, which is in turn overlain by two palaeosol layers: a light-brown, fine-grained palaeosol and a red, fine-grained palaeosol Finally, the Kızılkaya ignimbrite sits at the top

of this section

3.3 Yeşilhisar Section

At the base of this section is the Yeşilhisar conglomerate, which contains ophiolitic and metamorphic rock fragments within a silty to sandy matrix This unit is overlain by lacustrine sediments, beginning with greenish-grey, medium-grained sandstone and continuing sequentially upward with grey siltstone, greenish-grey sandstone, siltstone, pinkish-grey mudstone and grey sandstone horizons Up to this level, the lacustrine sediments are mainly greenish-grey and grey They continue upward with a level of pinkish-brown conglomerate, with a fine-grained matrix, then ignimbritic sandstone, mudstone, fine-grained conglomerate, sandstone (Figure 4f-g) and siltstone layers The Cemilköy ignimbrite sits at the top of this section

3.4 Akköy Section

This section has ophiolitic rocks (Figure 4h) at its base These are overlain by the Erdemisin agglomerate, and the Kavak ignimbrite, which comprises volcanic agglomerates, and pumiceous and vitric tuffites This unit is overlain by lacustrine sediments, comprising pumiceous claystone and sandstone beds (AK-2, AK-3, AK-4) and these sediments are overlain by the pale grey Cemilköy ignimbrite which contains lithic pumice This unit is overlain by palaeosol beds intercalated with conglomerate and fluvial sandstone beds The Kızılkaya ignimbrite sits at the top of this section

3.5 Erdemli Section

The Erdemisin agglomerate at the base of this section (Figure 4i), comprises abundant basaltic rock fragments and marl-rich sediments, and is overlain by lacustrine claystone beds and the pale grey Cemilköy ignimbrite This unit is in turn overlain by palaeosol (E-1, E-2) and white tuffite beds, and the section continues upward with more palaeosol layers, which are overlain by fluvial channel

Figure 1 Simplified geological map of the Araplı-Erdemli area of the Ürgüp Basin

(modified from Pasquaré 1968).

settlement fault

Kayseri Study area

100 km Mediterranean Sea

T U R K E Y Erdemli section

Akköy section

Araplı I

Yeşilhisar section

Erdemli

Keşlik

Araplı

Kurt Mt.

Küçükkurt H.

Akköy

Büyükkale H.

Kaleköy

scree slopes alluvium Kızılkaya ignimbrite Çataltepe basalt Gördeles ignimbrite Tahar ignimbrite Cemilköy ignimbrite

Mustafapaşa member Kavak ignimbrite Bayramhacılı member

Erdemisin agglomerate

auQ

unconformity unconformity

unconformity

Büyükkale tepe andesite

Yeşilhisar conglomerate ophiolitic complex

N

EXPLANATION

YEŞİLHİSAR

sediments (Figure 4j), sandstones and conglomeratic

units These are overlain by palaeosol horizons, and the

Tahar ignimbrite overlies the former units as three flow

units The Tahar ignimbrite is overlain by a brown, massive

palaeosol horizon which is intercalated with two layers of

fine-grained, brown, red-clay-pellet-bearing palaeosols

This unit is in turn overlain by a massive, white limestone

horizon and pale grey, coarse-grained pumice and

lithic-fragment-bearing lahar deposits This series is overlain by

the Kızılkaya ignimbrite, and a basaltic flow unit at the top

of this section

4 Lithofacies Distribution

Eight lithofacies have been distinguished within the Late

Miocene sediments of the Araplı-Erdemli area; these

lithofacies are adapted from Miall (1996; Figure 3) Basement rocks in the study area are metamorphic and ophiolitic rocks

4.1 Erdemisin Agglomerate (EA)

The Erdemisin agglomerate is the first product of Neogene volcanic activity in the study area It comprises volcanic agglomerates, pumiceous and vitric tuffites, and marl-rich sediments The cobbles in the unit are set in a greenish-grey

or violet tuffaceous matrix containing clayey arenaceous components consisting of grey andesitic and ophiolitic rock fragments (Pasquaré 1968)

4.2 Yeşilhisar Conglomerate (YC)

The Yeşilhisar conglomerate consists of thick-bedded fluvial sediments It almost entirely comprises more-or-less cemented conglomerates Pebbles of metamorphic and ophiolitic rock are rounded and vary in diameter from

a few mm to 20-30 cm

4.3 Conglomerate (C)

This facies is characterised by massive, grey, unsorted and sub-rounded conglomerates The conglomerate is mainly matrix-supported The average clast size is 10 cm, and measured profiles range from 20 – 50 cm thick Palaeoflow direction is generally from south to north

4.4 Sandstone (St)

This facies comprises greenish-grey, medium- to fine-grained, medium-bedded sandstone with plant rootlets This unit also encloses gypsiferous claystone intercalations

4.5 Mudstone (Mt)

This facies occurs at two levels: the lower unit is generally greenish-grey claystone, and the upper unit is generally brownish red It also encloses plant rootlets and desiccation cracks

4.6 Ignimbrite (I)

Four different ignimbrite members of the Ürgüp Formation have been examined in the study area:

The Cemilköy ignimbrite consists of white, massive

or thick-bedded lahar deposits with lithic, vitric and pumiceous fragments of ignimbritic origin (Pasquaré 1968)

The Tahar ignimbrite is represented by thick-bedded pinkish tuffite and fine lahar deposits of ignimbritic derivation (Pasquaré 1968)

The Gördeles ignimbrite consists of thick-bedded pink

to white ignimbrite, which passes laterally into a tuffite of similar composition (Pasquaré 1968)

The Kızılkaya ignimbrite is a single pinkish, well-welded columnar flow unit (Temel 1992)

4.7 Fallout (FO)

This facies is represented by two white fallout levels, comprising more than 80% pumice

4.8 Palaeosol (P)

The palaeosol can be considered to be aridisol (Soil Survey Staff 1975) Based on the system outlined by Retallack

İncesu ignimbrite (2.8 My) Seksenveren lavas Kızılkaya ignimbrite (4.3 My) Catal tepe lavas

double mass flow Gördeles ignimbrite (5.7 My) Tahar ignimbrite (5.8 My) double pumice fallout mass flow

Cemilköy ignimbrite (6.6 My)

Topuz dağı lavas Salur conglomerate Damsa valley lavas Sarımaden ignimbrite (8.2 My)

(9.0 My) Kavak ignimbrite

(11.2 My)

Güvercinlik ignimbrite (10 My)

Zelve ignimbrite (8.8 My) Mustafapaşa member

40m

P, L, D, F

P, L, D, F

P, L, D, F

P, L, D, F

P, L, D, F

P, L, D, F

P, L, D, F

P, F

P, F

P, F

P, F

L, F

En Yaşlı [oldest] ignimbrite (11 My)

Figure 2 Generalised stratigraphic section of the study area

(modified after Viereck et al 2010) P: palaeosol, L: carbonate, D:

diatomite, F: fluvial sediments.

Figure 3 Distribution of the principal lithologies of the Araplı-Erdemli areas (see Figure 1 for section

locations, and Table 1 for mineralogical compositions of the samples).

2 m

2m

Cemilköy ignimbrite

fallout II fallout

Silt

Silt

SiltS

Gra vel

Mud

Mud

Mud

Gra vel

Gra vel

Gra vel

Mud

Gra vel

Cemilköy ignimbrite Kavak ignimbrite Kızılkaya ignimbrite

Cemilköy ignimbrite Tahar ignimbrite

2 m

2 m

2 m

YH-10

YH-12 YH-13 YH-14 YT-2 YT-1

i

f

g

c

d

e

altered ignimbrite ignimbrite

ignimbrite

mudstone

vertisol

conglomerate

agglomerate basalt

j palaeosol

fluvial sediments ophiolite

Figure 4 Field view of: (a) Cemilköy ignimbrite, (b) altered Cemilköy ignimbrite, (c) contact relationship between

the Mustafapaşa member and Cemilköy ignimbrite, (d) vertisol levels, (e) mature-type developed palaeosols, (f) sandstone levels of the Mustafapaşa member, (g) conglomerate level of the Mustafapaşa member, (h) ophiolitic rocks, (i) Erdemisin agglomerate, (j) fluvial-channel deposits and mature developed palaeosol level.

d

plagioclase

volcanic glass chloritised pyroxene

serpentinised olivine

serpentinised olivine

pyroxene

clay organic

organic

organic organic

c

0.2 mm 0.1 mm

0.2 mm

0.2 mm 0.1 mm

0.2 mm

0.1 mm

plagioclase

oxypyroxene

clay + calcite

sesquioxides

oxyhornblende

Figure 5 Photomicrographs of (a) serpentinized olivine crystal (AK-1, plane polarised light), (b)

serpentinized olivine crystal (AK-1, plane polarised light), (c) alteration and chloritization of pyroxene

crystal (AK-1, YH-1 and YH-2, in-plane polarised light), (d) plagioclase (andesine) and amphibole

phenocrysts in volcanic-glass matrix (AK-1, YT-1 and YT-2, crossed nicols), (e-g) palaeosol samples,

sesquioxide and organic material bearing and resembling highly altered volcanic units with irregular

clay materials, plane polarised light, (h) ultramafic and volcanic rock fragments, feldspar, pyroxene,

amphibole, cemented by clay, sesquioxides and microsparitic calcite in sandstone (AK-8, crossed nicols)

(1988), these palaeosols can be roughly classified as poorly

to moderately developed, mature-type palaeosols The

palaeosol layers also enclose scattered pumice pebbles,

in contrast to the root zones in near-surface mature

palaeosols, and subsurface clayey, sesquioxide-rich areas

have developed The most mature soils are associated with

fluvial overbank deposits at some distance from the main

channels, which were the source of incremental additions

of fine-grained sediments Overbank deposits proximal

to palaeochannels have better-preserved bedding and less

mature palaeosols, and pedogenic disruption of bedding

and palaeosol maturity increase away from the channels

toward more distal floodplain settings

5 Methods

In the field, typical stratigraphic sections were measured

in order to study lateral and vertical variations within the

Late Cretaceous ophiolitic complex, the Oligo-Miocene

Yeşilhisar conglomerate and the Late Miocene fluvial and

lacustrine deposits interbedded with ignimbrites and lava

flows Forty-six characteristic samples of Oligo-Miocene

Yeşilhisar conglomerate, Late Miocene fluvio-lacustrine

sediments and associated palaeosols were collected from

the study area (Figure 3) Lithofacies definitions are based

on those of Miall (1996) Thin sections were prepared from

them to describe their petrographic properties

The mineralogical characteristics of the samples were

determined by X-ray powder diffractometry (XRD)

(Rigaku Geigerflex) and scanning electron microscopy

(SEM-EDX) (JEOL JSM 84A-EDX) Representative

palaeosol samples were prepared for clay-mineral analysis

(size fraction <2 µm) by separation of the clay fraction

by sedimentation, followed by centrifugation of the

suspension after dispersion overnight in distilled water

The clay particles were dispersed by ultrasonic vibration

for about 15 min Three oriented specimens of the <2

µm fraction of each sample were prepared by air drying,

ethylene-glycol solvation at 60 °C for 2 h, and thermal

treatment at 550°C for 2 h Semi-quantitative estimates

of the rock-forming minerals were obtained by using the

external standard method of Brindley (1980), whereas

the relative abundances of clay-mineral fractions were

determined using their basal reflections and the mineral

intensity factors of Moore and Reynolds (1989)

Representative clay-dominated bulk samples were

prepared for SEM analysis by sticking the fresh, broken

surface of each sample onto an aluminum sample holder

with double-sided tape and thinly coating (350 Å) with

gold using a Giko ion coater

Chemical analyses of 19 altered and fresh whole-rock

samples were performed at Acme Analytical Laboratories

Ltd (Canada) using ICP-AES for major and trace elements

and ICP-MS for rare-earth elements (REE) The detection

limits for the analyses were between 0.01 and 0.1 wt% for major elements, 0.1 and 5 ppm for trace elements, and 0.01

to 0.5 ppm for REE

6 Results 6.1 Petrography

The ophiolitic unit in the Araplı area comprises olivine and pyroxene Olivine crystals are mostly serpentinised (Figure 5a, b), and pyroxene crystals exhibit alteration and chloritization (Figure 5c) The Yeşilhisar conglomerate pebble samples from the Kaleköy and Akköy areas (AK-1, YT-1 and YT-2) generally consist of volcanic and ophiolitic rock fragments; in which amphiboles and pyroxenes are iron oxidised and chloritized Volcanic fragments consist

of plagioclase (andesine) and amphibole phenocrysts in a volcanic-glass matrix (Figure 5d)

Glass shards are generally devitrified whereas pyroxene crystals are highly altered and chloritized, and plagioclase and K-feldspar are partially to completely altered The matrix between these particles and minerals comprises volcanic materials and alteration products

In thin section, palaeosol samples were found to consist of devitrified volcanic glass and altered-feldspar-bearing, iron-oxidised amphibole and pyroxene and organic materials, thus resembling highly altered volcanic units (Figure 5e-g)

Sandstone contains pyroxene, amphibole, feldspar, clay and sesquioxides (Figure 5h) Conglomerates consist

of rounded and subrounded rock fragments cemented by sparry calcite crystals, similar to those reported by Siesser

(1973), and Kadir et al (2002)

6.2 XRD determinations

The results of X-ray diffraction analyses of samples collected from the Araplı, Yeşilhisar, Akköy, and Erdemli sections are presented in Table 1 The Araplı area rocks are characterised by abundant feldspar, quartz and opal-CT accompanied by accessory amphibole and serpentine in some levels of this section Smectite and chlorite occur in all levels, and coexist with kaolinite in some layers (Table 1) Correlation of these values with Table 2 indicate that the palaeosol in Araplı - Section I can be classified as oxisol (kaolinite, goethite, hematite), vertisol (smectite) and entisol (clay minerals related to the host rock)

The Mustafapaşa member is characterised by smectite + feldspar, and the weathered Cemilköy ignimbrite by a kaolinite + smectite + feldspar paragenesis

The Erdemli area is represented by a section between the Cemilköy and Kızılkaya ignimbrites The lithological and mineralogical character of the Erdemli area rocks is similar to that of the Araplı section rocks Feldspar, quartz, opal-CT and, locally, amphibole predominate Smectite and illite occur in all levels, and locally are accompanied

by kaolinite

The Akköy area rocks are characterised by abundant

feldspar, quartz and opal-CT in all levels of the profile

Amphibole is concentrated in some levels Smectite, illite

and chlorite are unevenly distributed

Smectite was determined by a peak at 14.9 Å, and

which expanded to 17.1 Å following ethylene glycolation;

the intensity of this peak collapsed to 10.04 Å following

heating to 550 °C (2 h) (Figure 6) The d 060 reflection of

smectite is 1.49 Å, revealing its dioctahedral character

Illite is indicated by reflections at 10 and 5 Å, and accessory chlorite by peaks at 14.1, 7.12 and 3.54 Å Quartz was determined by sharp peaks at 3.34 and 4.26 Å, and feldspar

by sharp peaks at 3.18 and 3.21 Å Accessory amphibole was distinguished by its weak peak at 8.4 Å and opal-CT

by peaks at 4.05 and 4.09 Å A slight increase in the XRD background of some of the smectite-bearing palaeosol samples may indicate the presence of organic material and poorly crystalline phases, as determined by textural

Table 1 Mineralogical variation within the CVP area.

smc: smectite, chl: chlorite, sep: sepiolite, kao: kaolinite, ill: illite, fds: feldspar, qtz: quartz, op: opal-CT, amph: amphibole, serp: serpentine, cal: calcite, dol: dolomite, tlc: talc, acc: accessory, +: relative abundance of mineral.

features and micromorphological images using

polarized-light microscopy and scanning electron microscopy

6.3 SEM determinations

SEM observations reveal that rod-like and nodular

volcanic glass can be generally characterised as devitrified,

and feldspar is highly altered (Figure 7a,b) Flaky smectite

has concentric morphology around casts that developed

by dissolution of rounded to sub-rounded volcanic glass

particles (Figure 7b,c) Authigenic smectite flakes occur as

microfracture-fillings (Figure 7d) and as cement among

relict volcanic glass shards and feldspar grains (Figure

7e) The sizes of smectite flakes generally increase from

the fracture margins toward their centres Flaky smectite

plates are mostly edged by fan-like forms which resemble

illite (Figure 7b-f) Locally, vermiform kaolinite rims

volcanic materials, and rosette-shaped chlorite occurs as

coatings on volcanic glass particles and altered feldspar grains (Figure 7g,h)

6.4 Geochemistry

The results of representative chemical analyses of samples collected from the Araplı I, Araplı II, Akköy and Erdemli sections are given in Table 2 These units contain major oxides in the following ranges: Al2O3 (10.31%–18.01%);

Fe2O3 (1.74%–8.70%); SiO2 (37.42%–71.89%); and loss on ignition (LOI) (4.60%–21.09%) Increases in LOI and clay-mineral content are important indicators of alteration The totals for Al2O3+Fe2O3 are low, and for SiO2 high in the lacustrine-sediment samples relative to the Cemilköy, Gördeles and Tahar ignimbrite samples These values reflect abundant smectite associated with quartz in the lacustrine deposits, and with kaolinite in these ignimbrites Sample A2.1, collected from clay levels of lacustrine deposits in

Table 2 Major- (wt.%) and trace-element (ppm) compositions of various lithologies of the study area (see Table 1 for the

mineralogical compositions of the samples).

Major Oxides/

Araplı Gördeles ign.

A1-8

Cr2O3 0.105 <0.001 0.007 0.014 0.046 0.011 <0.001 0.058 0.03 0.001 0.03 0.04

ign : ignimbrite, palaeo : palaeosol, sandst : sandstone, cong : conglomerate